Move dataclass to dedicated module

[LecrisUT]

A few reasons for this move:

• It would make migrating to attrs more easy #2831
• Plugin developers should use the same dataclass type
• This would allow some neat customization, e.g. if we add https://github.com/rr-/docstring_parser, we can move the help to the attribute's docsting

A few things to point out:

• All dataclass and field usage are now unified and populate the metadata. In principle this should be fine since it would just populate a field that would never be used, but should we do something else there to distinguish between DataContainer type of dataclasses and plain dataclass like the ones in hardware.py?
• The import syntax is a bit disjoint. The naming of dataclasses and the from import is done like this in order to minimize the diffs for the purpose of initial review, but I think we should change it to be more uniform w.r.t. full name tmt.dataclasses.dataclass vs short name field

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Pull Request Checklist

• [x] implement the feature
• [ ] write the documentation